Method of producing titanium



Aug. 19, 1958 W. H. KELLER EIAL METHOD OF PRODUCING TITANIUM Filed NOV.22, I954 Ti Sponge NuCX+ Ticx INVENTORS My K (6} BY Irwin 6'. 20m:

@Mw N ATTORNEY United States METHOD OF PRODUCING TITANIUM Wayne H.Keller, Waban, and Irwin S. Zonis, Belmont, Mass, assignors to NationalResearch Corporation, Cambridge, Mass., a corporation of MassachusettsApplication November 22, 1954, Serial No. 470,453

8 Claims. (Cl. 75-845) This invention relates to the production oftitanium and more particularly to the production of titanium by aprocess wherein a titanium compound is dissolved in a fused salt and isreduced to crystalline titanium metal by the addition of a molten metalreducing agent. This application is, in part, a continuation of ourcopending application Serial No. 373,512, filed August 11, 1953, and is,in part, a continuation of our copending application Serial No. 434,648,filed June 4, 1954.

Our aforesaid applications disclose a process for producing high yieldsof crystalline titanium wherein a molten reducing agent is fed to theupper surface of a'molten bath of a lower halide of titanium dissolvedin a fused salt. The process is so conducted as to form at the outset athin crust of sintered titanium fines over the bath, adhering to thewalls of the container and any other supporting structure that may bepresent. This porous layer of sintered fines acts as a barrier forsegregating on its upper side a layer of fused salt in which thereducing agent is concentrated but in which the titanium halide contentis low, this layer grading into the remainder of the bath in which therelative concentrations of re ducing agent and titanium halide arereversed. This concentration gradient is maintained through theremainder of the process andv constitutes an important condition of itsoperation. The sintered porous titanium barrier further performs theimportant function of a supporting bed from which titanium crystals growdownwardly into the titanium-halide-rich portion of the bath as theprocess continues.

An object of this invention is to provide a specific embodiment of theaforesaid process wherein the portion of the bath in which the reducingagent is concentrated may be maintained interiorly of the bath and belowits surface, extending into the lower portion of the bath so that thetitanium halide content of the bath may be more completely andefficiently utilized in the crystal growing operation. Another object isto provide such an embodiment in which the' reducing agent may be'moreefficiently distributed through the portion of the fused salt bath whichis substantially free of titanium halide. Other objects and advantageswill be apparent from the ensuing detailed description, taken inconnection with the accompanying drawing, the figure of which is adiagrammatic, schematic drawing illustrating one embodiment of theinvention;

For simplicity of description and without intent to limit the inventionthereby, it will be assumed, in the following discussion of theinvention, that the reducing agent is sodium, that the titanium lowerhalide is a titanium lower chloride, and that the fused salt is sodiumchloride. In accordance with our present invention, a foraminous shieldor barrier is provided extending vertically within the fused salt bath.This shield either itself surroundsor, in combination with a wallportion, segregates a portion of 'the bath into which liquid sodium isfed. Preferably this shield takes the form of a cylinder, hemisphere orthe like, open-at the top and extending down into the bath from aboveits upper surface. Preferably also it is of metal and may be formed ofsintered titanium fines or sponge. The liquid sodium feed tubepreferably extends downwardly within the portion of the bath segregatedby the shield to adjacent its lowermost portion.

The portion of the bath segregated by the shield constitutes essentiallymolten sodium chloride and the sodium fed thereto has little or notitanium chloride content. This may be accomplished initially by fillingthe area within the shield with a solid plug of sodium chloride which ismelted after fused sodium chloride (with dis-- solved titanium lowerchloride) is fed into the surround ing portion of the container. Theforaminous shield then prevents substantial circulation of titaniumchloride into the fused sodium chloride in its interior. Alternatively,the portion of the bath segregated by the shield may initially have thesame concentration of titanium lower chloride as the remainder of thebath. Inthis case, the initial feed of sodium into this portion of thebath soon eliminates substantially all of the titanium chloride thereinby reaction therewith to form titanium fines, these fines either sinkingto the bottom of this portion or adhering to the shield as a porous,spongy layer.

As the feed of the sodium continues, the sodium concentration of thisportion of the bath approaches saturation, and a sodium concentrationgradient is established through the shield to the surrounding portion ofthe bath. Hence, the conditions for crystal growth as described in ouraforesaid prior-applications are established. The crystals growoutwardly from the exterior of the shield or from a layer of titaniumsponge which may initially form thereover. Thus the shield acts as asupporting bed from which the crystals grow.

Since the point of sodium feed is preferably adjacent the bottom of thebath, the maintenance of a nearly saturated solution of sodium in sodiumchloride is promoted and crystal growing conditions are establishedthroughout the depth of the bath, thus providing efficient utilizationof the entire titanium lower halide content within the bath outside theshield. Furthermore, the portion of the bath within the shield may bestirred to promote a thorough circulation and distribution of the sodiumtherein.

If desired, feed of sodium within the shield may be supplemented by feedof sodium also to the upper surface of the bath outside the shield. Inthis case, there will be established on the upper surface of the bath aporous layer of titanium sponge between the shield and the containerwall, the sponge layer serving to segregate above it a layer of fusedsalt high in sodium and low in titanium chloride. Crystal growth fromthe lower portion of this horizontally extending sponge layer canproceed simultaneously with the growth of crystals outwardly from theshield.

Referring now to the drawing, there is illustrated one method ofpracticing the invention wherein 10 represents the reactor containing acharge of fused salt 12, this fused salt 12 preferably comprising sodiumchloride and containing a dissolved mixture of titanium dichloride andtitanium trichloride. Positioned within the fused salt bath is a hollowperforated body 14, in the form of a vertically extending cylinder,which is preferably tained essentially free of titanium chlorides,atleast.

after the reduction reaction has proceeded for a short period of time. Afeed pipe 20 is provided for feeding sodium near the bottom of cylinder14, excess sodium floating to the surface as indicated at 22. A stirrer24 Fatented Aug. 19, 1958 carried by a shaft 26 is preferably includedfor assisting in dissolving the sodium within the space 18. Rods or fins28 may be provided on the outside of the cylinder 14 to assist insupporting the growing mass of titanium crystals 30. As shown in thedrawing, each of the holes 16 is filled by a thin layer of titaniumsponge 30a serving as a porous diaphragm for isolating thetitaniumchloride-free salt 18 from the titanium-chride-containing salt12.

In the operation of the device illustrated in the drawing, the cylinder14 is positioned in the reaction chamber 10. In one method of operation,this cylinder 14. is initially filled with a solid casting of sodiumchloride. A molten mixture of sodium chloride and titanium lowerchlorides (trichloride and dichloride) is then poured into the reactorto about the level indicated, this mixture preferably being formed bythe partial reduction of titanium tetrachloride with sodium.

This molten mixture is preferably prepared in a separate reactor byreacting 1.7 moles of sodium with each mole of titanium tetrachloride toform a solution of titanium lower chlorides in sodium chloride. Theresultant titanium chloride content (excluding the byproduct sodiumchloride) is approximately 30 mole percent titanium trichloride and 70mole percent titanium dichloride. This relatively high proportion oftitanium trichloride has been found highly desirable, since equilibriumstudies indicate that the relative concentration of titanium trichloridein the mixture of titanium chlorides should be greater than about 11mole percent. If this it not done, there is a possibility of producingsome free titanium metal in the form of powder suspended in the fusedsalt. This free titanium powder can sinter to pipe walls and the likeand drastically affect the flow of fused salt. However, if the titaniumtrichloride concentration (relative to the dichloride) is maintainedabove about 11 mole percent, any free titanium produced will besubsequently consumed by reaction with the titanium trichloride.

This molten mixture is preferably at a temperature of about 850 C. to950 C. and will melt the sodium chloride inside the cylinder 14 so thatthe perforated cylinder 14 will thus at least initially separate anessentially titanium-chloride-free salt mass from a mass of saltcontaining dissolved titanium chloride. Sodium is then fed to theinterior of the cylinder, the sodium going into solution and diflusingoutwardly through the holes 16. As the sodium diffuses outwardly, itwill meet inwardly diffusing titanium chloride with which it will reactto form titanium powder. Since this powder will beformed at the holes16, it will rapidly collect around these holes 16 to form a partiallysintered sponge 30a, the sintered sponge serving to prevent gross how ofsalt inwardly or outwardly through these holes while permittingdiffusion of ions therethrough. Further feed of sodium to the thusisolated interior of cylinder 14 will provide a high concentration ofdissolved sodium adjacent the inner side of the porous sponge 30a. Thisconcentration gradient will decrease outwardly through the holes 16,thereby establishing conditions for the growth of large crystals.Titanium crystals of large size will accordingly start to form on theoutside of the sponge 30a, these titanium crystals forming an interlacedmass which, in itself, will provide an additional barrier to grosscirculation of the solution adjacent the outer surface of the cylinder14. The growing mass of crystals 'will then also aid in maintaining thesodium concentration gradient, this gradient extending graduallyoutwardly from the cylinder as the crystals grow thereon. Accordingly,the growing mass of crystals can additionally serve as an extension ofthe initial permeable titanium layer, thus permitting the sodiumconcentration gradient to be carried out into points of the bath farremoved from the perforated titanium cylinder 14. During the latterstages of the run, some circulation of the titanium dichloride solutionmay be employed to assure substantial utilization of the dissolvedtitanium dichloride. When the reduction has been completed, a frozensalt plug (indicated at 32 at the bottom of the reactor) may be meltedto allow drainage of the spent salt therefrom. This drains the greatbulk of the salt away from the titanium crystal mass, this mass thenbeing cooled and leached in acidified water to remove residual salt andany nnreacted reactants such as the lower chlorides of titanium andsodium.

In our process, as previously noted, the porous shield or barrier whichat least includes titanium fines and which produces a concentrationgradient of reducing agent in the fused salt plays an important part.This shield not only acts as a crystal growing bed and support but alsoappears to function as a distributor for the reducing agent to the zoneof crystal growth in such manner that crystal formation proceeds at arate considerably faster than can be accounted for by the moleculardiifusion rate of the reducing agent in fused salt. The crystal growthis also accomplished without substantial formation of free titaniumfines in the bath once the crystal growing starts. Localization of thereducing agent in the zone of crystal growth can be accounted for by thefact that the reducing agent must initially pass through the shield orbarrier from which the crystals grow, but the speed of thereactionindicates that the barrier supplements this function with some furtheraction in distributing and directing the reducing agent to the locale ofthe crystal growing.

The mass transported in a fluid system by simple molecular diffusion canbe expressed as mass transported per unit area per unit time under unitconcentration gradient across unit distance. This quantity is called thediffusion coeflicient and is a constant for a given system depending onviscosity, temperature, pressure, etc. A consideration of the basicproperties of the liquid Na1NaCl system leads to a calculated value inthe range of 10- to 10 for the molecular diffusion coeflicient of sodiumthrough sodium chloride. However, a series of experiments of the rate oftransport of sodium through sodium chloride in a metal tube indicatedthat the observed transport of sodium at 850 C, under the conditions ofour invention, is on the order of 10 to 10- which is one to two ordersof magnitude greater than that calculated for molecular dilfusion.Additionally, this observed sodium transport is not constant but isdependent on experimental conditions which have no appreciable effectupon the molecular diffusion coefficient.

In these experiments, nickel tubes were mounted vertically in a furnace.The tubes were filled with molten sodium chloride and on top of thesodium chloride there was provided a layer of moltensodium. Accordingly,the nickel tubes spanned a concentration gradient of sodium in sodiumchloride. At the end of predetermined periods of time, thebottom'portions of the tubes were pinched off and separated from theremainder of the tubes. The salt in these bottom portions was thenanalyzed for metallic sodium content. From the actual sodium content,apparent diffusion coefficients were calculated as follows:

Inner Difiusion Apparent Tube Length, cm. Tube Time, Difiusion Diameter,seconds Coefficient, inches cmF/sec.

3, 600 0.0055 /10 900 0.0110 345 3, 600 0.0070 /l6 14, 400 0. 0039 As 3,600 0. 0095 %o 14, 400 0. 0060 1- 3, 600 0. 0076 hundred times theestimated molecular difiusion coefiicient. There are also otheranomalies in these data. Thus the apparent diffusion coeflicient isfound to vary with the time available for transport and is also afunction of the length of the path available for transport and the tubediameter.

This dependence of the apparent diffusion coeflicient on time anddistance is not characteristic of molecular diffusion. However, thesevariations in sodium transport are compatible with the rate at whichsodium can be generated at a distance, assuming electrochemicalreactions at the walls of the tubes and subsequent electron transport bythe walls. The observed rate of transport of sodium and the observedvariations in the rate of transport both approximately fit anelectrochemical mechanism. Thus, in the sodium diffusion experiments,the

rate of transport of sodium down the tube and of chloride ions from thebottom to the top of the tube is consistent with rates which would beexperienced in a concentration cell, with an electrical potentialdifference between salt saturated with sodium at the top and saltcontaining less sodium at the bottom.

In such a concentration cell, electrons are furnished at the top of thecell (c. g., the nickel tube) by ionization of dissolved sodium, theseelectrons traveling down the tube and liberating sodium at the points oflower sodium concentration. The resultant excess negative chloride ionsat the bottom of the cell and positive sodium ions at the top of thecell will migrate toward each other. Since the migration of sodium ionsand chloride ions in the existing electrical potential difference ismuch faster than molecular diffusion of sodium, the above-postulatedconcentration cell mechanism can explain a transport of sodium which ismuch faster than would be indicated if true molecular diffusion werecontrolling.

Comparing the tubes in the foregoing experiments with the network ofcores in the shield or barrier, it will be apparent that a positivesodium distributing action is indicated for the barrier. If thetransport of sodium through the porous barrier operates at least in partby electron transfer, the mechanism would be as follows: Due to. theconcentration gradient of sodium between the saturated solution ofsodium in sodium chloride and the solution of titanium chloride insodium chloride, an electrical potential difference is set up in thefused salt bath. This electrical potential difference is similar to theelectrical potential difference existing in the simple sodiumconcentration cell since the concentration of sodium in the titaniumchloride solution is very low. The electrons resulting from theionization of dissolved sodium are conducted by the metal of thebarrier, under the influence of the electrical potential difierence, topoints in the titanium chloride solution where the electrons may act tocause deposit of titanium atoms. The electrons can deposit titaniumeither directly or indirectly by release of sodium atoms which in turnreact with titanium chloride to deposit metallic titanium on thebarrier.

Since the barrier is porous, chloride ions and sodium ions are free tomigrate therethrough, these ions traveling under the existing potentialdifference at a much higher rate of speed than in true moleculardiffusion. As the titanium crystals grow on the barrier, these crystalsin turn act as an extension of the barrier so that electrons can becarried to the farthest tips of the growing crystals. Observed titaniumproduction rates, wherein sodium was introduced on one side of a porousbarrier and titanium crystals were grown on the other side of thebarrier, have been compared with theoretical titanium production rates,assuming the transport of sodium by the concentration cell mechanism.The actual titanium production rates were of the same order of magnitudeas the calculated rates based on this theoretical mechanism.

While we are not certain of the exact mechanism of sodium transportaccomplished by the porous barrier, it could be either a surface wettingtransfer or the abovediscussed electron transfer or perhaps acombination of 6 both. Sodium contacting the metal surface of thebarrier could, by wetting action on that surface, migrate down- Wardlyand outwardly over the forming crystals. This would also tend to directsodium feed to the point of crystal growth.

While a specific example of the invention has been discussed above,numerous alternative embodiments of the described apparatus and processmay be employed without departing from the spirit of the invention. Thebarrier or shield 14, for example, can be a fine mesh screen or asintered titanium sponge. Equally, the barrier 14 can be modifiedgreatly. For example, it can be rectangular in cross section or of anyother convenient shape. More than one feed tube can be provided for eachbarrier if so desired. Other shapes and dimensions for the barrier canobviously be employed, as well as using a plurality of such barrierelements for each fused salt bath. The temperature of the reaction massmay be varied widely from slightly above the melting point of the saltto temperatures on the order of 1000 C. and above. Numerous reducingagents other than the sodium may be employed. For example, potassium,calcium, magnesium, lithium or various combinations of these elementsmay be utilized. From the standpoint of low cost of operation, sodium ormagnesium is preferred. Other halides of titanium may be utilizedalthough, from the standpoint of cost, ease of handling, etc., thetetrachloride is preferred as starting material.

The process may be practiced with continuous or intermittent feed oftitanium chloride, either as such or dissolved in fused salt. In suchcase, an intermittent or continuous overflow of fused product salt willnormally be provided at a point in the reactor where the fused salt isrelatively low in titanium chloride. While agitation of the titaniumchloride bath should be minimized, particularly while the initialsintered titanium layer is forming, some slight circulation of the bathmay be provided at later stages of the process to facilitate completereaction between the contained titanium chlorides and sodium.

Additionally, the reactor can be fed with lower halides of titanium suchas titanium trichloride, manufactured from titanium-bearing materials inthe manner shown in the copending applications of Singleton, Serial No.304,- 388, filed August 14, 1952, now Patent No. 2,770,541, grantedNovember 13, 1956, and Singleton, Serial No. 315,461, filed October 18,1952, now abandoned. Equally, titanium trichloride can be made by thetechnique described by Sherfey et al., Journal of Research of the Bureauof Standards 46, 299-300, April 1951. Additionally, the dichloride oftitanium can be manufactured by numerous processes such asdisproportionation of the trichloride or partial reduction of thetrichloride or tetrachloride.

The present invention can be equally employed for the manufacture oftitanium alloys by the coreduction of the chlorides, for example, ofvanadium, chromium, manganese, iron, nickel, cobalt, columbium,tantalum, molybdenum, tungsten or silicon. The alloy may be a binaryalloy or it may be an alloy containing 3 or 4 constituents. In themanufacture of alloys, the same general conditions are employed.Accordingly, when the expression titanium is used in the appendedclaims, it is intended to include alloys of titanium as well as puretitanium.

It should be additionally pointed out that the salt mixture in which thereduction is carried out may be formed of numerous halides which can bemixed halides, single halides and halides of materials other than thespecific reducing agent or agents employed in the reaction. From thestandpoint of simplicity of operation and ease of control, it ispreferred, however, that the salt be the chloride of the reducing agent.Thus it is quite feasible to employ binary and ternary mixtures ofhalides having quite low melting points.

It should be pointed out, in connection with a consideration of thevarious salts which can be employed, that these salts should becompletely anhydrous and free of any contaminants such as carbon,nitrogen, oxygen or hydrogen. This is due to the tremendous reactivityof titanium metal at temperatures on the order of 800 C. to 900 C. andabove.

In the above specification, reference has been made particularly to thepreferred titanium chloride, tetrachloride and dichloride. In mostinstances, the trichloride is equally useful and, as a matter of fact,it is extremely unlikely that any system having an appreciableconcentration of one of the lower chlorides of titanium will not have atleast some of the other lower chloride also present. It should beapparent that one can also employ the corresponding di-, triandtetra-halides from the group consisting of the iodides, bromides andfluorides of titanium.

Since certain changes may be made in the above proceSs without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description, or shown in the accompanyingdrawing, shall be interpreted'as illustrative and not in a limitingsense.

What is claimed is:

l. in the process of forming titanium crystals by the reduction of alower titanium chloride dissolved in an inert fused salt, theimprovement which comprises feeding reducing agent to a portion of thesalt which is substantially free of lower titanium chloride andisolating said portion from the remainder of the bath by means of agenerally vertically extending foraminous shield which prevents rapidfiow of fused salt between said portion and the remainder of the bathcontaining lower titanium chloride. the reducing agent being fed to aportion of the salt which is substantially below the surface thereof soas to substantially saturate the portion of the fused salt to which thereducing agent is fed, the forarninous shield serving as a barrier forsegregating on one side thereof the high concentration of reducing agentin the fused salt which is substantially free of titanium chloride, thishigh concentration of reducing agent grading into the remainder of thefused salt in which the relative concentrations of reducing agent andtitanium chloride are reversed.

2. A process for manufacturing titanium wherein a titanium lowerchloride is dissolved in a bath of an inert fused salt and is reduced totitanium crystals 'by the addition of a metallic reducing agent, theimprovement of which comprises providing and maintaining in the fusedsalt bath a zone comprising fused salt substantially free of titaniumlower chloride, said zone being laterally displaced from the portion. ofthe fused salt containing dissolved titanium chloride and being isolatedfrom said tanium-chloride-containing portion of the fused salt bath bymeans of a generally vertically extending permeable metallic diaphragm,and supplying reducing agent to said zone so as to substantiallysaturate said zone to which the reducing agent is fed, the diaphragmserving as a barrier for segregating on one side thereof the highconcentration of reducing agent in the fused salt which is substantiallyfree of titanium chlorides, this high concentration of reducing agentgrading into the remainder of the fused salt in which the relativeconcentrations of reducing agent and titanium lower chloride arereversed.

3. In a process of forming titanium crystals by the reduction of a lowertitanium chloride dissolved in an inert fused salt, the improvementwhich comprises pro viding in a fused salt a foraminous layer comprisingtitanium particles which extends from adjacent the surface of the bathdownwardly an appreciable depth into the bath, and feeding reducingagent to the fused salt bath on one side of the titanium layer toprovide a zone which is substantially saturated with reducing agent toform reducing agent concentration gradient which extends generallyhorizontally through said layer, said layer serv ing to prevent rapidflow of fused salt from one side fused salt :to which the reducing agentis fed, this high concentration of reducing agent grading into the remainder of the bath in which the relative concentrations of reducingagent and titanium chloride are reversed.

4. A process for manufacturing titanium wherein a titanium lowerchloride is dissolved in a bath of an inert fused salt and is reduced totitanium crystals by the addition of a metallic reducing agent, theimprovement of hich comprises providing and maintaining in the fusedbath a porous metallic element between the point of reducing agent feedand the remaining portion of the bath, the feed of reducing agent beingbelow the surface of the fused salt to a portion of the fused salt whichis substantially free of titanium chloride and the porous metallicelement being elfective to maintain a generally horizontally extendingconcentration gradient of reducing agent, said porous metallic elementsegregating on one side thereof a high concentration of reducing agentand substantially no titanium chloride in the portion of the fused saltbath to which the reducing agent is fed, this high concentration ofreducing agent grading into :the .remainder of the bath in which therelative concentrations of reducing agent and titanium chloride arereversed.

5. in a process for producing titanium wherein a lower halide oftitanium is dissolved in an inert fused salt bath and is reduced totitanium crystals by means of a metallic reducing agent selected fromthe class consistingof the alkali metals and the alkaline earth metals,the molten salt comprising a halide selected from the group consistingof the alkali metal halides and the alkalineearth metal halides, theimprovement which comprises adding molten reducing agent to a limitedportion of the fused salt bath, maintaining said limited portionessentially free of dissolved titanium lower halide, said limitedportion extending a substantial distance down into said bath, isolatingsaid limited portion from the remainder of the bath containing titaniumlower halide at least partially by means of a vertically extending layerof sintered titani urn particles, said vertically extending layer ofsintered titanium particles segregating on one side thereof a highconcentration of reducing agent and substantially no titanium lowerhalide in the portion of the fused salt bath to which the reducing agentis fed, this concentration of reducing agent grading into the remainderof the bath in which the relative concentrations of reducing agent andtitanium lower halide are reversed.

6. In a process for manufacturing titanium wherein a solution of a lowerchloride of titanium in an inert molten salt is reduced to metallictitanium by means of sodium, the improvement which comprises feeding thesodium to a limited portion of the molten salt to form an initialvertically extending layer of sintered titanium particles whichseparates the limited portion of the salt from the remainder thereof,the layer of titanium particles being effective to prevent rapid flow ofsalt through the layer so as to permit the formation of a sodiumconcentration gradient which extends horizontally across the layer,feeding more sodium to the limited portion of the molten salt bath tomaintain the sodium concentration gradient, this concentration gradienttraveling horizontally away from the point of sodium feed as a mass oftitanium crystals forms on the far side of the initial titanium layer inthe portion of the molten salt bath containing lower titanium chloride,and supporting the initial titanium layer in the position Where it wasformed in the salt bath during reduction of further titanium chloridewithin the salt bath, said vertically extending layer of sinteredtitanium particles segregating on one.

side thereof a high concentration of reducing agent and substantially notitaniumlower chloride in the portionof.

the fused salt bath to which the reducing agent is fed, theconcentration of reducing agent grading into the remainder of the bathin which the relative concentrations of reducing agent and titaniumchloride are reversed.

7. The process of claim 2 wherein the reducing agent comprises sodium,the lower titanium chloride comprises a mixture of titanium dichlorideand titanium trichloride dissolved in sodium chloride, and the molepercentage of titanium trichloride relative to the titanium dichloridecontent is at least 11 percent at the start of the feed of sodium to thefused salt.

8. The process of claim 2 wherein the zone comprising fused salt low intitanium lower chloride is agitated to increase dissolution of thereducing agent in the fused salt in said zone.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN THE PROCESS OF FORMING TITANIUM CRYSTALS BY THE REDUCTION OF ALOWER TITANIUM CHLORIDE DISSOLVED IN AN INERT FUSED SALT, THEIMPROVEMENT WHICH COMPRISES FEEDING REDUCING AGENT TO A PORTION OF THESALT WHICH IS SUBSTANTIALLY FREE OF LOWER TITANIUM CHLORIDE ANDISOLATING SAID PORTION FROM THE REMAINDER OF THE BATH BY MEANS OF AGENERALLY VERTICALLY EXTENDING FORAMINOUS SHIELD WHICH PREVENTS RAPEDFLOW OF FUSED SALT BETWEEN SAID PORTION AND THE REMAINDER OF THE BATHCONTAINING LOWER TITANIUM CHLORIDE, THE REDUCING AGENT BEING FED TO APORTION OF THE SALT WHICH IS SUBSTANTIALLY BELOW THE SURFACE THEREOF SOAS TO SUBSTANTIALLY SATURATE THE PORTION OF THE FUSED SALT TO WHICH THEREDUCING AGENT ISE FED, THE FORAMINOUS SHIELD SERVING AS A BARRIER FORSEGREGATING ON ONE SIDE THEREOF THE HIGH CONCENTRATION OF REDUCING AGENTIN THE FUSED SALT WHICH IS SUBSTANTIALLY FREE OF TITANIUM CHLORIDE, THISHIGH CONCENTRATION OF REDUCING AGENT GRADING INTO THE REMAINDER OF THEFUSED SALT IN WHICH THE RELATIVE CONCENTTATIONS OF REDUCING AGENT ANDTITANIUM CHLORIDE ARE REVERSED.